Waves Flashcards
(26 cards)
What is a progressive wave?
Carries energy from one place to another without transferring any material
How do waves work?
Waves cause the particles of the medium they travel through to oscillate
Relationship between frequency and time period
F is 1 over time
What is phase difference?
The amount by which one wave lags behind another
What is significant about EM waves?
They all have the same speed when in a vacuum
What is a transverse wave?
The displacement of the particles is right angled (perpendicular) to the direction of energy propagation all EM are transverse
What are longitudinal waves ?
Waves with displacement of particles going along (parallel) to the direction of energy propagation (a sound wave consists of alternative compressions and rare fractions of the medium it’s travelling through)
Can longitudinal waves be polarised?
No
What is a polarised wave?
A wave that oscillates in one direction only, in one plane
How do polarising filters work?
Polarisation filters a transverse wave so that it’s oscillations only occur in one plane (any other plane won’t pass through), if two polarising filters are placed at right angles to each other, no light will pass through
What discovery did polarisation lead to?
That light waves are transfers and not longitudinal since only transverse waves can be polarised
What are 2 real world examples of polarisation?
1) glare reduction (light reflected off of surfaces become partially polarised, this light can be polarised through a filter at right angle reducing intensity of light entering your eye)
2) TV and Radio signals (orientation of rods on the transmitting aerial have to be aligned)
What is superposition?
When two or more waves cross, the restaurant displacement equals the vector sum of the individual displacements
What is the difference between constructive and deconstructive interference?
Constructive the waves combine but deconstructive the waves cancel out
What is a stationary wave
It is the superposition of two progressive waves with the same frequency or wavelength and amplitude, moving in opposite directions (no energy transmitted by a stationary wave)
Difference between the first and the second harmonic?
First has only two nodes made up of half a wavelength compared to sec on which is made up of two half wavelengths and 3 nodes. Second harmonic has twice the frequency.
For each harmonic what does the frequency change by?
Each time frequency is multiplied by number of harmonics.
Where is a node and where is the antinode?
Node is when displacement is at zero and antinode is at maximum displacement
What is the resonant frequency?
The frequency at which a stationary wave is formed
What is diffraction?
The way that waves spread out as they come through a narrow gap or go round obstacles (when gap bigger than wavelength diffraction unnoticeable where is of it’s same size it’s at a maximum and then if gap is smaller than wavelength most waves are reflected back )
Describe the single slit diffraction pattern
Central maximum is twice as wide and brightest part of the pattern, this is wider and all maxima either side of centre progressively get dimmer and narrower (more closely spaced)
What is intensity?
Power per unit area
What affects the width of the central maximum ?
1) Increasing the slit width will decrease the amount of diffraction meaning central maximum is narrower but increased intensity
2) Increasing the wavelength will increase diffraction meaning central maximum is wider and intensity is lower
What does coherent mean?
Two waves must have same wavelength and frequency and a fixed phases difference between them (troughs line up causing constructive interference and a very intense beam)
